Non-transferred arc torch process and apparatus



C6942 xR 298749265 Feb. 17,1959 -1'. a. REED ETAL 2,874,265

NON-TRANSFERRED ARC 'roacn PROCESS AND ummus H I Filed lay 23, 1956 v)LA' {:2-

Water f F M l Torch T h 0' r 3 Q are me non Generator 0 E ElectrodeHolder I 20 Electrode 1 18" Nozzle N l "2% Wafer 23 24 25 Cuflmg Jet 'lKerf Work INVENTORS THOMAS B. REED JOHN MAIERJII GLENN w. OYLER A TTORNEV United States Patent 0 Non-mammalian sac 'roncn rnocms ANDarranarus 'lhomasB.Reed,GrandIsland,N.Y andJohnMalerIIl,

Newark, and Glenn w. Oyler, sit-m ans, N. 1., as-

?ors to Union Carbide Corporation, a corporation New York'lhisinventionrelatestoconstrictedarcsofthetype disclosed in copendingapplications Serial No. 524,353, filed July 26, 1955, now Patent No.2,806,124, dated September 10, 1957, and Serial No. 539,794, filedOctober 11, 1955, by Robert M. Gage; the present application being acontinuation-in-part of our application Serial No. 540,951, filedOctober 17, 1955.

According to the present invention we provide a major advance in the artwhich comprises discharging selected gas heated by a constricted are ata velocity in the sonic range toward a work area. The heat transferintensity of the resultant efliuent from the torch with hydrogen is suchthat it is possible, for example, cleanly to cut a 0.09 inch kerf(dross-free) at 30 inches per minute in one inch thick aluminum platenot in electrical circuit relation with such arc. Since the work neednot be in circuit with the arc the invention is useful also for cuttingnon-metals, as well as other purposes such asspalling rock..

As used herein the term sonic range includes velocities of 0.5 Machnumber or greater. The term Mach number refers to the ratio of thelinear gas velocity to the velocity of sound in the same gas for thegiven temperature and gas composition.

More particularly, we provide a novel process of producing a very hightemperature, high intensity jet or effiuent which comprises deliveringhydrogen gas to the inlet of an orifice of a nonle under pressure,discharging the gas through such orifice at sonic velocity, andmaintaining a high pressure are in such orifice.

An important parameter in industrial heating applications, such ascutting, welding, gouging, piercing or spelling, is the heat transferintensity of the heat source. As one proceeds, for example, from aBunsen burner to a blowtorch to an oxy-gas flame to a jet burner, onefinds new heating processes possible at each step of increased heattransfer intensity. The flame temperatures of the above devices varyonly by a factor of about 2, but the arc flame intensity varies 'by afactor of about 100, as shown in Table I below. This table also showsthat the process of our invention provides a heat source having a heattransfer intensity which is more than 14 times greater than anypreviously available (jet burner). In particular, this new highintensity obtained with our inven- Typical Usesoft solder. silversolder.

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2,874,265 Patented Feb. 17,v 1959 tion makes it possible to cut thicksections of any common metal or nonmetal with a quality and speedcomparable and often exceeding that of cutting of steelby theoxy-acetylene process.

The intensity of a flame is determined both by the temperature (or moreproperly heat content) of the hot gases, and by the rate at which thegases are delivered to the surface being heated (i. e., the fiamevelocity). Thus: I(intensity of eflluent)=V(veloci y) Xh(heat content)in cal./cm.' sec. Such formula will be explained more fully below.

The present invention attains high heat transfer intensity by passinghydrogen gas at sonic velocity or higher through a constricted aremaintained between a central pencil-type electrode and a nonleelectrode.

An essential feature of such are torch is that it employs a nozzleelectrode which is non-consumable and has an orifice through which thetorch gas is discharged and into which the arc plasma is forced. Thenozzle electrode is so constructed that the maximum effective crosssection of the orifice must have an area which is no larger than thatwhich will wall-stabilize the are. This are stabilintion occurs due tothe torch gas stream forcing the arc plasma down into the orifice so asto be adjacent to the orifice walls. The nozzle is cooled so that itwill both remain unconsumed and effectively stabilize the arc. Becauseof its being cold relative to the temperature of the gas passing throughit, its length should be limited to not more than about six such minimumdihelium and oxygen as meters or it will rob heat unnecessarily from theeflluent.

We have found, however, that one-half to three times the minimumdiameter of the orifice provides a satisfactory length thereof.According to our invention, a refractory nonle metal, such as tungsten,is preferred for longer life of an insert or of the nozzle itself.

Since the arc is carried between electrodes in the torch body, and sincethe work is not an arc electrode, it is necessary that the energydeveloped by our torch be transported to the work entirely by theeflluent. Because of its unique properties hydrogen gas is preferred byus as the efiluent.

The properties of hydrogen which are believed to explain its exceptionalutility for our purpose in the are torch are: (l) for a given current,more heat is put into the gas as the hydrogen content is increased,because the voltage drop across the gas increases with the hydrogenaddition; (2) the low molecular weight of hydrogen gives much highervelocities than other common gases to the eflluent for a given pressuredrop across the nozzle, and the rate of delivery of thermal energy fromthe arc to the work varies directly with that velocity; and (3) thediatomic hydrogen molecule is dissociated at are temperatures formingatomic hydrogen which upon' recombining gives up large quantities ofheat to the work.

Alternative that can be used instead of or mixed wimgi f c mmemou-arenitrogen,

turesthereof,suc "am' ma.

wing the 1:1 e Wiagrammatic view illustrating the invention, the torchand work being shown in cross section.

As shown therein, the torch 10 comprises a cylindrical body 12containing a water-cooled electrode holder 14 in which is mounted anelongated electrode 1. A

-- metal nozzle 18 is screwed in the end of the body 12.

The nozzle has an inner chamber 20 that is provided with a taperedportion 21 leading to an orifice 23 in axial alignment with theelectrode 16. The nozzle also is provided with an annular cooling-waterpassage 24 surrounding the orifice, to which water is delivered anddischarged through an inlet 25 and an outlet 21. Gas is delivered underpressure to the chamber 2. through a pipeZinthewallofthetorchbodylZ.

The electrodel is connected to one terminal of a suitable source ofelectrical power, such as a D. C. welding generator 30, by a conductor32. The other termias! of such generator is connected to the nozzle 18by a conductor 34. Thus, in this arrangement the electrode1istheeathode,andthenozzle18istheanodeofa high pressure are 35 which isenergized therebetween by 4 gen is better by a factor of two than-anyother gas. In order to get the high velocity shown in Table II, a nonlecross sectional area is chosen, so that gas volume at arctemp./area=velocity, and generally this will give rather small diameternonles (A inch din.) with the electrical power available from singlecommercial power sources. Naturally, if several generators are connectedtogether, greater power is available and larger diameter orifices can beemployed.

TABLE II Theoretical heat transfer intensity from sonic lets at are orflame temperatures flaatamperaturelnanarcwhcelnthelmtsed,thsstlgureswtllbedlflcmt,bnt same the generator 30. Such are andthe gas supplied to the chamber are forced through and discharge fromthe orifice asaietSCofVeryhoLeflluentgas at sonic velocity.

Incutting work38with theiet36,thetorchlland work 38 are moved relativelyone to the other along the desired path of cut, so that the jet rapidlyremoves material therefrom, forming a kerf 40 in such work.

The construction of the torch wherein the electrodes liand llareassembledwith aclosed ehamberfor thearcgasprovidesboththatthegaspassingthroughthetorchlicanbecontrolledinits that bypressurizingthegasinsuchehamberthevelocityofthe emuentconsistingofietualsocanbecontrolled. Thisisofgreatestimportancewhenitisdesiredtotransporttheenergyoftheietmostrapidlyforsuchusesasthe severing ofmetals.

It has been stated above that the heat transfer intensityofaheatsourceis determined by the velocity, V,ofthegasesintheflameandbytheheatcontenthofthegases (as computed from thermalproperties thereof) accordingtotherelatioslhip cal. 1 r-vs at mThrsisthe flux 'intheflameitself. as

determines iet velocities. Since the velocity of sound in a gas isproportional to the square root of temperatureandinverselyproportionaltothesquarerootofthe molecular weight, it isadvantageous to choose a high temperature and a low molecular weight toget the highestVinFormula Landthisvelocityandthc productVlsanlistedin'l'ablell. Thistableshowsthathydro- 1hasbeenused'tocutM-inchthickstainlesssteelplate In order to obtain ahigh flame intensity, Formula 1 I able ability of the non-transferredarc torch to melt tsahontl (It A practical measure of heat intensity canbe obtained using the device herein described. If one subtracts theamount of heat lost in the cooling water from that entering the torchelectrically, one obtains the heat transferred to the gas. Dividing thisby the noule area gives flame intensity. This is listed in several ofthe examples. The intensities of flames can be measured similarly,knowing fuel consumption and eficiency, and nozzle area and heat loss.,Asanesampleoftheuseoftheprinciplesdiscussed above, we can mention arctorch cutting. In this process, according to our invention, anon-transferred arc and the resulting jet of gases develop heretoforeunknown heat transfer intensities suficient to melt metals or non-metalsin a narrow slit or kerf at a very high rate are made possible. Usingthe non-transferred torch with a tungsten nonle, l-in. thick aluminumplate was cut ,at30I.P.M.and l-in.stainlesssteelplateat6I.P.M.

as per the following Examples I and II.

wtthatungsteninsertaboutfi -inlongwithaflow-in.diameteruialholewssusedwith 142C.F.H.ofhydrogen, 15.5 p. s. i. g.chamber pressure at 215 amperes, and 93 volts D. C. between the tungstencathode and the acute, the resulting arc-jet issuing from the nozzleorifice was effective in cutting bin. thick aluminum plate at 30 I. P.M., producing a high quality, straight-walled ke'f.

' ml? II The same torch described in Example I above, except that thetungsten nozrle insert was l/s-in. long and had a hi -in. diameterorifice, was used with 100 C. F. H. hydrogen, chamber pressure 23 p. s.i. g., and 170 peres, 84 volts, D. C. power, producing a hydrogenetlluent that was used to cut l-in. thick stainless plate at 6 I. P. M.The cut was very square at the and the kerf surfaces were remarkablysmooth.

The discussion and examples above show the E ii! cut materials whenemploying hydrogen gas.

Thenon-uansferredarctorchwithhydrogengas sEE . 548inchesperminuteaceordingtothefollowingeaample:

EXAHPLI In The arch torch comprised a ri-in. diameter tungsten rodcathode mounted concentric with and set back %-in. from a tungsten anodenonle Si -in. inside diameter by fi -in. long. The tungsten anode nonlewas made from a %-in. diameter round and was press-inserted in thewater-cooled copper torch chamber. A supersonic jet effiuent of atomichydrogen was produced by pressurizing the torch chamber with hydrogenwas produced by pressurizing the torch chamber with hydrogen gas at 23p. s. i. gage and heating the gas with a power are of 170 amperes at 84volts direct current between the tungsten rod and nozzle electrodes. Thehydrogen gas flow through the torch was 100 C. F. H. measured at roomtemperature and atmospheric pressure. The supersonic atomic hydrogen jetemuent produced a good quality cut through Vs-in. thick stainless steelplate at a speed of 48 inches per minute. The torch-to-plate disstancewas about %-in. The are power was 14,300 wattsandofthis9.400wasinthegasandtheremainderappeared in the cooling water,producing an efliciency of 65%, and an intensity of 114 kcaL/cm. see.

What is claimed is:

1. Process which comprises energin'ng a high pressure are between twoelectrodes one of which is provided with gases selected tr It nsrstrngof by men, nitrogmflr n guchofihome some range thereof, whereby anintense jet-like diluent is produced which fiows from such orifice atsuch velocity, characterized in that such are is wall-stabilized in suchprocess. 1

LPrOcessasdefinedbyclaim Linwhichsuchgas produces at sonic velocity aminimum heat transfer intensity of the order of 40 lrcaL/cm. sec,characterized in that such are is wall-stabilized in such process.

3. Process as defined by claim 2, in which the gas is of essentiallyhydrogen.

4. A sonic jet non-transferred arc torch apparatuscomprising,ineomibnation,meansprovidingagaschamber,

6 anozzleconnectedtosaidmeanasaidnouiehavingan orifice, the maximumefiective cross-sectional area of such orifice being no greater thanthat of a natural are at the same current level; an electrode mounted onsaid means in line with such orifice, means for supplying a selected gasto said chamber for discharge through such orifice at a velocity in thesonic range, and means for energizing a high pressure are between saidelectrode and said nozzle, whereby such arc and gas are forced throughsuch orifice, wall-stabilized and discharged therefrom as a jet-likeetliuent at a velocity in the sonic range thereof.

5. A non-transferred arc torch as defined by claim 4 provided withwater-cooled means for discharging through such wall-stabilizing arcconstricting orifice a high pressure are and gas selected to produce anintense jet of efliuent at sonic velocity having a heat transferintensity I of more than the order of 40 when I==Vh (veloeityXheatcontent) 5% 6. Process for cutting metals which comprises feeding hdroencontainin gas around a stick electrode and ge in another electrode,establishing an are between said stick electrode and said nozzleelectrode, projecting said are into the passage of said nozzle electrodeso that it is at least partially wellstabilized thereby, dischargingtherefrom a jet-like etfiuent of hot hydrogen gas at a velocity above0.5 Mach, the shape and cross section of said efiiuent being controlledby said nozzle electrode, and applying said efliuent to a metal body toform therein a narrow (of the order of 0.09 inch wide) dross-free kerfhaving relatively straight and smooth walls.

References Cited in the file of this patent UNITED STATES PATENTS1,002,721 Mflthers Sept. 5, 1911 1,746,191 Devers Feb. 4, 1930 1,746,196Langmuir et a1. Feb. 4, 1930 2,768,279 Rava Oct. 23, 1956

